This protein work has established six important points. First, there is extensive differentiation within electrophoretic alleles, and the evidence suggests that selection and drift act jointly at a single locus. Second, there is no detailed congruence between cytological and genetic relationships, chiefly because ancestral alleles are retained haphazardly. Third, many polymorphisms have been retained for at least fifteen million years and must have persisted through selection. Fourth, the two phylads of the virilis group evolved at different rates, with the ecologically conservative virilis phylad evolving more slowly than the opportunistic montana phylad. The average lineage of the virilis phylad added alleles at nine loci at the rate of 0.69 per million years, and the montana added them at a rate of 1.01 per million years. Fifth, "absolute" rates of genic evolution have been calculated. For the group as a whole these range from 0.0 to 0.44 per locus per million years. Some loci evolved at different rates in the different phylads. Hence the molecular clock is not reliable and these data do not support the premise of the neutralist theory that molecular evolution proceeds at a constant rate for a given protein. Sixth, these studies provide no evidence for extensive reorganization of the gene pool during speciation. I propose to extend these findings with (1) an in depth investigation of differentiation within electrophoretic alleles locus by locus throughout the virilis groups and microgeographically within the species D. americana, (2) an expanded study of the historical development of gene pools emphasizing the different metabolic classes of loci to determine in what ways these differ evolutionarily, (3) a study of salivary gland chromosomes of new species and new populations to augment presently available cytological information, and (4) to develop methods for storing living Drosophila adults at low temperatures for long periods to reduce effort now required for maintaining large living collections of Drosophila.